//定义变量
@width:200px;
@height:200px;
@color:red;
  #box{
    position: absolute;
    left: 50%;
    top: 50%;
    width: @width;
    height: @height;
    margin-left: -@width/2;
    margin-top: -@height/2;
    border: 2px solid @color;
  }

